1. Field of the Invention
The invention relates to watertight structures, and more particularly, to a watertight structure implemented by tightening a mounting bolt.
2. Related Art
Conventionally, there is a switch in an automobile, which turns on or off a room lamp or the like as a door is opened or closed. This switch is provided to visibly warn the driver or the like that he or she has forgotten to close a door or that he or she has closed a door incompletely by causing the switch to turn off the room lamp or the like. More specifically, this switch is attached to a panel of the body of an automobile which confronts a door, and turns off an illuminating room lamp or the like when the distance between the door and the panel equals a predetermined value as the door is closed, i.e., when the distance equals such a value as to be judged that the door is completely closed. Since the switch is necessarily disposed in the vicinity of the door, water droplets are easy to deposit on the switch in rainy weather or the like. It is for this reason that watertightness is called for in both the switch and the mounting portion of the switch.
FIG. 3 shows such a switch. A switch insertion hole 11 and a screw hole 12 are formed in a panel 10 that serves as a fixed member of the body of an automobile which confronts a door (not shown). Part of a watertight switch (hereinafter referred to simply as the "switch") 20 is inserted into the switch insertion hole 11. The outer surface of the switch 20 projecting from the panel 10 is covered with a rubber cover 21 that serves as a watertight member, so that entrance of water droplets or the like into the inside of the panel 10 is prevented.
The switch 20 is roughly divided into two parts: a switch portion 22, and a mounting portion 23. The switch portion 22 has a projected portion 24 that projects in a vertical direction (projecting direction) from the outside of the panel 10. The projected portion 24 is formed so that the door abuts thereagainst. The projected portion 24 is thus biased by the door in a direction indicated by the arrow A when the door is closed. Further, inside the projected portion 24 is a movable contact 25, which is supported so as to vertically reciprocate with respect to the panel 10. The movable contact 25 is urged toward the outside of the panel 10 by the elasticity of an elastic body (not shown), e.g., a spring. When the projected portion 24 is biased in the direction indicated by the arrow A as the door has been closed, the movable contact 25 moves toward the inside of the panel 10 against the elasticity of the elastic body.
Further, the switch portion 22 has a fixed contact 26, and the fixed contact 26 confront the movable contact 25 at a distance therebetween. The fixed contact 26 is connected to an ECU (not shown) that is mounted on the vehicle through a connector 27 and that generally controls the vehicle. When the projected portion 24 is biased in the direction indicated by the arrow A by the door, the movable contact 25 moves toward the inside of the panel 10 together with the projected portion 24, and the movable contact 25 comes in contact with the fixed contact 26 when the distance between the door and the panel becomes equal to such a value as to be judged that the door has been completely closed.
The switch 20 has a switch bracket 28 formed in the rubber cover 21. The switch bracket 28 serves as a member to be fixed which extends from the switch portion 22 to the mounting portion 23. This switch bracket 28 is made of metal, and is electrically connected to the movable contact 25. It may be noted that the surface 10a of the panel 10 is provided with a coating (not shown), so that the switch bracket 28 and the panel 10 is insulated. The switch bracket 28 has a mounting hole 29 formed therein at the same position as the screw hole 12. A barring bent portion 29a is formed on the mounting hole 29 so that the barring bent portion 29a projects in a vertical direction from the outside of the panel 10 in annular form. The aperture of the barring bent portion 29a has substantially the same diameter as the screw hole 12. The barring bent portion 29a is formed by bending the switch bracket 28.
On the other hand, the mounting bolt 30 for fixing the switch 20 to the panel 10 is made of metal, and has a hexagonal tightening portion 30a formed on one end thereof so that the mounting bolt 30 can be tightened by a spanner or the like. A disclike flange portion 30b is integrally formed on the tightening portion 30a, the flange portion 30b having a diameter larger than the tightening portion 30a. The flange portion 30b comes in contact with the barring bent portion 29a at the time of tightening the mounting bolt 30. The switch bracket 28 is electrically connected to the body by the flange portion 30b through the mounting bolt 30 and the screw hole 12 of the panel 10 (body earth). That is, the movable contact 25 that is connected to the switch bracket 28 is electrically connected to the body. When the door has been completely closed, both the contacts 25, 26 of the switch 20 come in contact with each other as described above. Then, the switch 20 applies a signal indicating that the door has been completely closed to the ECU through the connector 27, and the ECU turns on the room lamp or the like based on such signal.
As shown in FIG. 4, a seal portion 21a, which is an annular projected portion, is formed on the rubber cover 21 that is put around the outer circumference of the barring bent portion 29a in such a manner that the seal portion 21a becomes higher than the barring bent portion 29a in annular form. As shown in FIG. 3, the flange portion 30b of the mounting bolt 30 not only comes in contact with the barring bent portion 29a but also compresses the seal portion 21a so as to be in intimate contact therewith at the time of tightening the mounting bolt 30. Therefore, entrance of water droplets or the like from the vicinity of the mounting bolt 30 is prevented.
However, since the barring bent portion 29a is formed by bending the switch bracket 28 made of metal as described above, it is not possible to bend the metal at a right angle. Therefore, a gap S is produced between the barring bent portion 29a and the mounting bolt 30 as shown in FIG. 3. Further, the mounting bolt 30 is such that the movement of the flange portion thereof toward the inside of the panel 10 is regulated by the barring bent portion 29a. As a result, when the mounting bolt 30 is tightened excessively, the panel 10 close to the screw hole 12 may, in some cases, be drawn into the gap S between the barring bent portion 29a and the mounting bolt 30. As a result, the panel 10 is deformed as shown in FIG. 5, and water droplets or the like may, in some cases, enter into the panel 10 from such deformed portion.